The present invention relates to a method and system for counting tracks of an optical disk, and more particularly to a track-counting method and system for use in sample servo type optical disk apparatus.
As one of tracking systems for the write-once type optical disk there is known the sample servo system as exemplified in FIG. 1. In FIG. 1, illustrated at numeral 1 is an optical disk having a number of data-recording tracks TR coaxially formed thereon. For access of an optical head 2 to a destination track (recording track with a predetermined address), an optical head drive section 4 is driven in accordance with a drive signal from a drive control section 3 to be moved radially with respect to the optical disk 1 so that the optical head 2 traverses the recording tracks one by one. The optical disk 1 rotates during this head-traversing operation whereby the optical head 2 picks up data from the optical disk 1 to output the pickup signal. A signal processing circuit 5 processes the pickup signal to obtain tracking information periodically outputted whenever the optical head 2 traverses each recording track TR, the tracking information being counted by a track-counting section 6 so as to count the number of the tracks TR. FIG. 2 is an illustration of a sample servo type disk recording system for describing the above-mentioned pickup signal. In FIG. 2, the recording area includes a pit region for a servo byte and a data region for recording data. In the pit region there are a pair of tracking signal pits
and PB provided at the positions offset by 1/4 pitch toward the inner side and outer side with respect to the center line of each of the recording tracks TR.sub.n+1, TRn, TR.sub.n-1, and there is further a clocking signal pit PC provided on the center line of each track. The optical head 2 successively illuminates these pits PA, PB and PC and receives the reflection light therefrom to pick up information signals. The pickup signals are supplied to the signal processing circuit 5 so as to be sampled and held on the basis of sampling pulses generated at the timing of the detections of the pits PA, PB and PC, thereby detecting the tracking information representing the position-shifted amount of the read light beam of the optical head 2 from the tracking signal pits PA and PB and further detecting the clock information indicating the timing that the read light beam from the optical head 2 passes on the clocking signal pit PC.
Here, for the servo byte system indicated in the pit region of FIG. 2, there has been proposed an access code region as shown in FIG. 3. That is, the successively arranged tracks are grouped into units each comprising 16 tracks, i.e., 0th track to 15th tracks numbered in order, which are indicated with 4 pits provided on the track center line. The 4 pits are provided in a space for allowing the provision of 11 pits and, of the 4 pits, 3 pits are provided at the similar positions to 3 pits of the adjacent track and 1 pit is provided at the different position from 1 pit of the adjacent track. In this case, if the disk is eccentrically deformed, there is the possibility that the optical head moves in the direction opposite to the normally track-counting direction, thereby making it difficult to accurately count the number of the tracks.